The cellular slime molds are model systems for the study of developmental biology. The research will be focused upon the differentiation of vegetative amoebae into two cell types, the prespore and prestalk cells which then form the mature spore and stalk cells composing a mature sorocarp. Adhesive contacts are attributed to surface antigens which may be qualitatively distinct on each cell type. Consequently, they may effect differentiation of the cell types during development. Fluorescent monoclonal antibodies will be used to detect changes in D. discoideum surface antigen throughout the aggregation phase and subsequent stages. Differentiation of aggregating amoebae bearing different complements of surface antigens would indicate the appearance of prestalk and prespore cells. The rate at which prespore and prestalk groups isolated from a slug synthesize new types of surface antigens on the two missing cell types will be determined. Prespore and prestalk cells will be dispersed into single cells to observe changes in their surface antigens as they differentiate. Vegetative amoebae, dispersed prestalk and prespore cells will be exposed to cyclic AMP to determine if it causes surface antigen changes. D. mucoroides prespore cells will be transplanted into the prestalk region to determine if it is necessary for them to migrate through the prespore-prestalk junction to form prestalk cells. By using partial barriers at the prespore or prestalk regions the patterns of redifferentiation in the slug cells will be studied. Grafts of thymidine-labeled D. micoroides prespores or small number of D. discoideum prespores onto the anterior half of a cold slug will reveal the patterns of cell movement and differentiation at different stages of development. Cell interactions are essential in the development of organisms. In humans, certain carcinomas tend to lose cell adhesiveness resulting in metastasis. This effect may be associated with the loss of glycoproteins from the cell surfaces. Research on Dictyostelium may yield information applicable to health problems in mankind.